Near field communication systems are more and more frequent and can be found in many applications.
Such systems use a radio frequency electromagnetic field emitted by a device (terminal or reader) to communicate with another device (card).
According to applications, a NFC device only communicates in card mode or the same NFC device can operate in card mode or in reader mode (for example, in the case of a near-field communication between two cellular phones).
When it operates in reader mode, a device generates a radio frequency electromagnetic field intended to be detected by devices present within its range (operating in card mode).
When it operates in card mode, a NFC device detects a radio frequency electromagnetic field generated by a device operating in reader mode. Certain devices (essentially so-called passive load modulation devices) sample the power necessary for their operation from the field radiated by a reader having them within its range and retro-modulate the field of the terminal. Other devices (with an active load modulation) have their own power source in order to be capable of transmitting a signal to respond to the reader in synchronized fashion.